Thermosetting coating compositions comprising hydroxy-functional epoxy-polyester graft copolymers and blocked polyisocyanates

ABSTRACT

An organic solvent based, thermosetting coating composition of a hydroxy functional epoxy-polyester graft copolymer and blocked polyisocyanate crosslinking agent. The coating composition may be formulated as a hot sprayable, high solids coating composition suitable for use as a chip resistant automotive vehicle primer adapted for use on body panel areas subject to chipping by stones, gravel and other road debris. Alternatively, the composition may be formulated as a high solids composition sprayable with conventional spraying equipment. Hydroxy functional epoxy-polyester graft copolymer is prepared by polymerization of lactone monomers in the presence of hydroxy functional epoxy ester resin precursor. Such precursor resin is formed by reaction of diepoxide chain extended substantially simultaneously with diphenol and dicarboxylic acid and chain terminated with acid component comprising primary hydroxy functional acid.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of Ser. No. 798,085 filedNov. 14, 1985, now U.S. Pat. No. 4,698,398.

Reference is made to concurrently filed and commonly assigned relatedU.S. applications Ser. No. 798,044 filed Nov. 14, 1985, now U.S. Pat.No. 4,708,995, entitled "Chip Resistant Primer Composition I" and Ser.No. 798,079 filed Nov. 14, 1985, now U.S. Pat. No. 4,698,399, entitled"Chip Resistant Primer Composition I'" both to Kordomenos et al.

TECHNICAL FIELD

This invention relates to a novel hydroxy functional epoxy-polyestergraft copolymer and to a novel, solvent-based, thermosetting coatingcomposition comprising same. It relates also to such coating compositionformulated, for example, as a hot sprayable, high solids coatingcomposition suitable for use as a chip resistant automotive vehicleprimer adapted for use on body panel areas subject to chipping bystones, gravel and other road debris.

BACKGROUND

Automobile manufacturers, in their efforts to extend the expected lifeof automobile sheet metal and the like, have directed considerableattention to various processes and compositions designed to result innot only improved corrosion resistance but also improved chip resistanceproperties. In particular, research and development efforts haverecently been directed to obtaining primer compositions which areflexible and chip resistant and which give corrosion protection whileexhibiting good humidity and solvent resistance, as well as goodintercoat adhesion. New automobile designs and concern about chipping inareas exposed to stones, gravel and other road debris, e.g. rockerpanels, have demanded such chip resistant primers which can be appliedin reasonable thicknesses by techniques which do not require extensiveand expensive processing modifications during painting operations. Todate available primers, whether high or low solids, have not provensuitable.

In order to overcome the aforementioned chipping problem it has beencommon to apply relatively thick chip resistant coatings in hody panelregions, which are inclined to chip, prior to application of stillanother primer composition. One such chip resistant sealer materialwhich has been employed is a polyvinyl chloride plastisol sealer whichhas been applied with airless spraygun equipment in thicknesses of about20 mils in regions subject to high levels of chipping. Problemsattendant with such thick coatings are readily apparent. Because of thethickness in the region to which it is applied, these materials presentan appearance problem often resulting in waviness and roughness in thefinal coating on the sheet metal. Often times surface imperfections alsoresult from the fact that a primer is applied over the top of thissealer, with the primer and sealer being cured together. As a resultsome solvent and plasticizer tend to be driven out of the polyvinylchloride plastisol and result in a wavy and rough surface. Still furtherproblems associated with the use of such polyvinyl chloride plastisolsealers and the like involve application technique. Since the polyvinylchloride plastisol sealers and the like must be applied in thicknessesof 20 mils or greater in order to obtain good adhesion, they cannot befeathered down to blend in with other regions of the sheet metal whichdo not require the additional chip protection. Thus, the materials mustbe applied using a masking technique whereby those regions which are notto be coated with the sealer material are masked in a separate operationprior to application of sealer. This masking is then removed after thesealer is applied. It would obviously be desirable to eliminate theseadditional steps in the application of the chip resistant sealermaterial.

Accordingly, it is a preferred object of this invention to provide anovel solvent based, thermosetting coating composition adapted for useas a chip resistant primer, which primer may be applied in thicknessesof less than 20 mils and which may be feathered in such a manner as toblend with paint in other areas of the substrate to be painted which donot require chip resistant coating.

It is a further object of the present invention to provide novel resinssuitable for use in solvent-based thermosetting coating compositions. Inthis regard, it is a particular object of the invention to providenovel, hydroxy functional epoxy-polyester graft copolymer resins whichare crosslinkable during cure, on the surface of a substrate.

It is another object of the invention to provide novel coatingcompositions which comprise crosslinkable hydroxy functionalepoxy-polyester graft copolymers and blocked polyisocyanate crosslinkingagent and which provide high crosslinking efficiency and tough, wellcured films at minimum bake temperatures such as when applied asautomotive primers. In this regard, it is a particular object of theinvention to provide a novel hydroxy functional epoxy-polyester/blockedpolyisocyanate thermosetting coating composition of sufficiently lowVolatile Organic Content (VOC) to aid in meeting governmental emissionsguidelines and yet which can be applied to a substrate by spraying orother known method.

It is another object of the invention to provide a composition whichwill form a coating on a substrate, which coating has advantageousphysical properties including, for example, humidity and solventresistance, flexibility and corrosion protection for the underlyingsubstrate.

Additional aspects and advantages of the invention will be apparent fromthe following description thereof.

DISCLOSURE OF THE INVENTION

According to the present invention, novel crosslinkable hydroxyfunctional epoxy-polyester graft copolymer resins are provided which aresuitable for use in thermosetting coating compositions, and which areespecially advantageous for use in high solids and chip resistant,organic solvent based thermosetting coating compositions. The hydroxyfunctional epoxy-polyester graft copolymer resins of the inventionpreferably have a number average molecular weight (Mn) of about 2,000 toabout 20,000 and are the product of polymerization of lactone monomersin the presence of hydroxy functional epoxy ester resin precursorpreferably having a number average molecular weight (Mn) of betweenabout 1,000 and about 4,000 and itself being the reaction product ofdiepoxide chain extended substantially simultaneously with diphenol anddicarboxylic acid and either subsequently or simultaneously chainterminated with acid component comprising primary hydroxy functionalacid. The diepoxide is reacted substantially simultaneously withdiphenol and dicarboxylic acid in amounts sufficient to give a weightper epoxide (WPE) of between about 500 and about 2,500, preferablybetween about 500 and about 1,500. Preferably the diphenol anddicarboxylic acid are employed in a ratio of 10/90 to 90/10 by weight.

Also according to the present invention, a novel, organic solvent based,thermosetting resin/crosslinking agent composition, in addition tosolvent and any pigments and additives such as, for example, catalyst,flow control agents and the like, comprises the hydroxy functionalepoxy-polyester graft copolymer resin of the invention and blockedpolyisocyanate crosslinking agent including, but not limited to, blockedtrifunctional isocyanurate ring containing polyisocyanates andoligoester modified blocked isocyanates.

Particularly preferred compositions of the invention are thoseformulated as high solids coating compositions having solids levels inthe range of 65-80% solids and which are applied as chip resistantprimers in those areas of automotive panels, such as rocker panels,which are exposed to high levels of chipping. Such compositions may beapplied in thicknesses ranging from 1 to 25 mils wet to obtain finalcoatings in the range of 1 to 12 mils dry, and may be feathered down toblend in with paint applied to regions outside that requiring additionalchip resistance protection. Generally, the compositions of this solidslevel may be applied using hot spray equipment at temperatures in therange of room temperature is about 25° C. to about 160° F.

Other preferred compositions of the invention are those formulated ashigh solids coating compositions adapted to be applied by conventionalspraying onto a substrate. These high solids coating compositions mayhave a solids level in the range of 50-60% and are especially useful asa primer coating on the bare, unpolished metal surface of an automotivevehicle. As used herein, a high solids coating composition is one havinga volatile organic content of about 479 g/l (4.0 lb./gal.) or less.

Other features and advantages of this invention will become moreapparent from the following, detailed description thereof including thepreferred embodiments and best mode of carrying out this invention.

DETAILED DESCRIPTION OF THE INVENTION

More specifically, the invention relates to a novel hydroxy functionalepoxy-polyester graft copolymer suitable for use in a thermosettingcomposition and to a thermosetting composition comprising that hydroxyfunctional graft copolymer and a blocked polyisocyanate crosslinkingagent.

The novel, epoxy-polyester graft copolymer preferably has a numberaverage molecular weight (Mn) of between about 2,000 and about 20,000and is the product of polymerization of lactone monomers in the presenceof hydroxy functional epoxy ester resin precursor preferably having anumber average molecular weight (Mn) of between about 1,000 and about4,000. The hydroxy functional epoxy ester resin precursor is thereaction product of diepoxide chain extended substantiallysimultaneously with diphenol and dicarboxylic acid and eithersubsequently or simultaneously chain terminated with acid componentcomprising primary hydroxy functional acid. The diphenol anddicarboxylic acid are reacted substantially simultaneously withdiepoxide in amounts sufficient to give a weight per epoxide (WPE) ofbetween about 500 and about 2,500, preferably between about 500 andabout 1,500. Preferably the diphenol and dicarboxylic acid are employedin a ratio of 10/90 to 90/10 weight. The polymerization of lactonemonomers with the precursor is carried out at a temperature betweenabout 50° C. and about 300° C., preferably at a temperature of betweenabout 130° C. and about 200° C., and the polymerization reaction mixturepreferably comprises between about 10 and about 80 weight percenthydroxy functional epoxy ester resin precursor and between about 90 andabout 20 weight percent lactone monomers. Preferably, the polymerizationreaction mixture comprises between about 35 and about 65 weight percenthydroxy functional epoxy ester resin precursor and between about 65 andabout 35 weight percent lactone monomers.

Thermosetting compositions of the invention comprise the above hydroxyfunctional graft copolymer and blocked polyisocyanate crosslinking agentcomprising at least two isocyanate groups which has been blocked byreaction with an active hydrogen bearing blocking agent. The blockedpolyisocyanate crosslinking agent is included in the composition in anamount such that upon deblocking of the blocked isocyanate groupsthereof at the cure temperature of the composition, the crosslinkingagent provides between about 0.5 and about 1.6 reactive isocyanategroups per reactive group on the hydroxy functional epoxy-polyestergraft copolymer.

Each of the above major components of the compositions as well as othercomponents and other aspects of the invention are described hereinafterin greater detail.

A. Hydroxy Functional Epoxy-Polyester Graft Copolymer

As described above this copolymer is the product of polymerization oflactone monomer in the presence of an hydroxy functional epoxy esterresin precursor which itself is the reaction product of diepoxide, whichhas been chain extended substantially simultaneously with diphenol anddicarboxylic acid, with hydroxy functional acid component comprisingprimary hydroxy functional acid in chain terminating reaction.

It is believed to be a significant characterizing aspect of the hydroxyfunctional epoxy-polyester graft copolymer of the invention that thepolymerized lactone portion of the hydroxy functional epoxy-polyestergraft copolymer gives the copolymer flexibility as well as toughness,two key properties when choosing a primer for use in areas susceptibleto chipping. It is a further characterizing aspect of the copolymer thatit includes epoxy resin portions, i.e. hydroxyl terminated epoxy esterresin precursor is used as an initiator to form the graft copolymer,which give the copolymer excellent corrosion resistance properties.Still further, because the graft copolymers of the invention arebranched, they require a minimum amount of crosslinking in order toobtain a suitable network for good coating integrity. Since crosslinkbonds, e.g. isocyanate bonds as used in compositions of the invention,tend to be somewhat brittle, it is desirable to keep the number of suchbonds to a minimum.

Preferred hydroxy functional epoxy-polyester graft copolymers of theinvention include significant aromatic content which is believed toenhance corrosion resistance properties. Even though aromatics tend toincrease the brittleness of polymers and compositions including suchpolymers, it is possible to include them since, as mentioned above, thepolymerized lactone portion of the hydroxy functional epoxy-polyestergraft copolymer gives the polymer increased flexibility which more thancompensates for any such brittleness. A particularly preferredembodiment of the hydroxy functional epoxy-polyester graft copolymerresin of the invention is prepared from aromatic containing diepoxide.Also, as discussed hereafter, the dicarboxylic acid reactant employed inpreparation of the hydroxy functional epoxy-ester resin precursor mayalso include aromatic units.

Each of the reactants employed in the preparation of the hydroxyfunctional epoxy-polyester graft copolymer is described in greaterdetail below.

(i) Diepoxide Reactant

The diepoxide reactant employed in the manufacture of the hydroxyfunctional epoxy ester resin precursor can be any of numerous diepoxidesincluding diphenol chain extended epoxides, many of which arecommercially available and which will be apparent to the skilled in theart in view of the present disclosure. While, ultimately, the choice ofthe diepoxide reactant for preparing the hydroxy functional epoxy esterresin precursor will depend to an extent upon the particular applicationintended for the coating composition, terminal diepoxides, that isdiepoxides bearing two terminal epoxide groups, are generally mostpreferred. These are generally more reactive and therefore requirereaction conditions under which undesirable side reactions, for example,epoxy-epoxy reactions and gellation, can be more easily avoided. Thediepoxides which are to be chain extended with the diphenol anddicarboxylic acid may be selected from numerous diepoxides, some ofwhich may be diphenol extended diepoxides.

Diepoxy resins, not previously extended with diphenol, may be used inthe preparation of the hydroxy functional epoxy ester resin precursor.Preferred diepoxy resins of this type include: Epon 828 (trademark) andEpon 829 (trademark), which are non-extended diepoxides of the Epon(trademark) Series, Shell Chemical Co., Houston, Tex., as well ascycloaliphatic diepoxy resins, such as the Eponex (trademark) series,Shell Chemical Company: hydantoin epoxy resins such as, for example,Resin XB2793 (trademark, Giba-Geigy Corporation, Ardsley, N.Y.); and anyof a wide variety of acyclic or cyclic aliphatic diepoxides such as, forexample, 1,4-butanediol diglycidyl ether and 4-vinylcyclohexene dioxideand the like. Still other suitable diepoxides which may be chainextended with dicarboxylic acid and used in synthesizing the epoxy-esterresin precursor are commercially available and will be apparent to theskilled of the art in view of the present disclosure.

Still further, diepoxides previously extended with diphenol may be usedin forming the precursor and numerous such materials are commerciallyavailable. These include certain of the well known bisphenol-Aepichlorohydrin epoxy resins of the aforementioned Epon (trademark)series, e.g. Epon 1000 and Epon 1004 and the DER (trademark) series, DowChemical Company, Midland, Mich., e.g., DER 332. These diglycidyl etherbisphenol-A resins or higher molecular weight analogs thereof, are mostpreferred in view of their cost and commercial availability.

Also, it will be understood from the foregoing that any mixture ofcompatible diepoxides may be used.

In addition to the diepoxide, a portion of the epoxy functionality canbe provided by any compatible monoepoxy compound or polyepoxy compoundor mixture of such compounds. The polyepoxide can be any of the wellknown types such as polyglycidyl ethers of polyphenols. These can beproduced by etherification of polyphenol with epihalohydrin in thepresence of alkali. It will be recognized by the skilled of the art inveiw of the present disclosure, that in some instances, particularlywhere a coating composition of high solids content is less important, itmay be desirable to incorporate polyepoxide of higher molecular weight.Preferably, any such polyepoxide contains free hydroxyl groups inaddition to epoxide groups.

While polyglycidyl ethers of polyphenol can be employed, it may bedesirable to react a portion of the reactive sites (hydroxyl or in someinstances epoxy) with a modifying material to vary the filmcharacteristics of the resin. The epoxy resin may be modified, forexample, with isocyanate group containing organic materials or otherreactive organic materials.

Other useful polyepoxides are the novolak resins including, for example,the novolak epoxy resins ECN 1235 (trademark) and ECN 1273 (trademark),Ciba-Geigy Corporation.

According to preferred embodiments of the present invention, epoxidecompounds other than diepoxide compounds provide no more than about 15%and most preferably substantially none of the total epoxidefunctionality in the reactants used to form the epoxy-ester resin.

(ii) Diphenol Reactant

The diphenol reactants suitable for reaction with the diepoxide reactantand dicarboxylic acid in chain extension reaction include numerouscommercially available materials, many of which will be readily apparentto the skilled of the art in view of the present disclosure. Preferreddiphenols have the general formula (I): ##STR1## wherein R is a divalentlinking moiety substantially unreactive with the diepoxide resin.Preferably R is a divalent organic linking moiety, for example (CH₂)_(n)where n is preferably from about 1 to about 8, C=O, and the like,although inorganic moieties, for example sulfonyl and the like, are alsosuitable. Diphenols of this character have been found to provide goodreactivity with diepoxides described above and to provide, ultimately,cured coatings of the invention having excellent physical properties,most notably excellent corrosion protection. It will be apparent to theskilled of the art in view of the present disclosure that R should besubstantially unreactive with the acid component employed in preparationof the epoxy ester resin precursor. Particularly preferred diphenolsinclude those according to formula (I) above, wherein R is selected fromthe group comprising a straight or branched alkylene or alkylidenemoiety of one to about 10 carbons, preferably having three to fourcarbons and most preferably having the general formula: ##STR2## whereinR' and R" are the same or different and each is a monovalent organicmoiety preferably selected from the group comprising hydrogen and loweralkyl of about one to four carbons, most preferably one or two carbons,and the like or a mixture of any of them. Preferably the diphenol has anumber average molecular weight (M_(n)) between about 180 and about 500,more preferably between about 180 and about 250. Such diphenols include,for example bisphenol-A, which is most preferred, bisphenol-B,bisphenol-F and a compatible mixture of any of them. As used herein theterm diphenol may include, for example, compounds comprising a singledihydroxy substituted phenyl ring such as benzenediol. More preferred,however, are those diphenols providing two terminal, mono-hydroxysubstituted phenyl rings such as in formula (I), above. Other examplesof diphenols are bis-(4-hydroxy-tertbutylphenyl)2,2-propane,bis-(hydroxy-naphthyl)-methane and 1,5-dihydroxynaphthalene. Othersuitable diphenols useful to form the epoxy ester resin of the presentinvention will be apparent to the skilled of the art in view of thepresent disclosure.

(iii) Dicarboxylic Acid Reactant

Dicarboxylic acids suitable for chain extending diepoxides discussedabove preferably have a number average molecular weight of between about145 and about 1000 and more preferably between about 400 and about 600.Suitable dicarboxylic acids includes numerous commercially availablematerials, many of which will be readily apparent to the skilled of theart in view of the present disclosure. Suitable dicarboxylic acidsinclude saturated or unsaturated, cyclic or acyclic, aliphatic oraromatic dicarboxylic acids or a mixture thereof. Acyclic aliphaticdicarboxylic acids are generally preferred in view of the enhancedflexibility they provide to the cured coatings of the invention.Preferred dicarboxylic acids have the general formula (II):

    HOOC--R"'--COOH                                            (II)

wherein R is a divalent linking moiety substantially unreactive with thediepoxide resin. It will be apparent to the skilled of the art in viewof the present disclosure, that R"' should be substantially unreactivealso with the acid component employed in preparation of the epoxy esterresin precursor, and with hydroxy functionality (generated in thechain-extension reaction). Preferably R"' is a divalent, organic,linking moiety. Particularly preferred are those dicarboxylic acidswherein R"' is selected from the group comprising a straight or branchedalkylene or alkylidene moiety, preferably of about 4-42 carbons, forexample, (CH₂)_(n) wherein n is preferably from about 4 to about 42, andthe like or a mixture thereof. Dicarboxylic acids of this character havebeen found to provide good reactivity with the preferred diepoxidesdescribed above and to provide, ultimately, cured coatings of theinvention having excellent physical properties, most notably excellentflexibility and corrosion protection.

Exemplary dicarboxylic acids include adipic acid,3,3-dimethylpentanedioic acid, benzenedicarboxylic acid,phenylenediethanoic acid, naphthalenedicarboxylic acid pimelic acid,suberic acid, azelaic acid, sebacic acid, and the like or a compatiblemixture of any of them. The anyhydrides of these acids, where theanhydrides exist, are, of course, embraced in the term "acid" since thereaction products obtained therefrom are the same. While dicarboxylicacids according to formula (II) can be used, wherein R"' is an alkylenechain of less than 4 carbons, for example, oxalic acid, malonic acid,succinic acid, glutaric acid and the like, these are less preferred inview of the somewhat lesser degree of flexibility provided thereby.Preferably the dicarboxylic acid provides two terminal carboxyl groups.Similarly, preferred aromatic dicarboxylic acids are those wherein thecarboxylic groups are more spaced apart, for example,1,4-benzenedicarboxylic acid and 2,7-naphthalenedicarboxylic acid.

The most preferred dicarboxylic acids are substantially saturated,acyclic, aliphatic dimer acids, which are well known to the skilled ofthe art and readily commercially available. These are typically thedimerization reaction products of fatty acids which have from 4 to 22carbons and a terminal carboxyl group. Of these, dimer acid of 36carbons is most preferred since it provides excellent reactivity withthe preferred diepoxides described above, provides epoxy ester reactionproducts of advantageously wide molecular weight distribution, andprovides, ultimately, cured coatings of the invention having excellentphysical properties. In addition, dimer acid of 36 carbons is readilycommercially available, for example, as Empol 1014 (trademark), Empol1016 (trademark) and Empol 1018 (trademark), each available from EmeryIndustries, Inc., Cincinnati, Ohio. It should be recognized that most orall commercially available dimer acids contain some portion of trimeracid, typically, for example, about 5-10% but in some cases as much as30% or more, and also contain a usually smaller portion ofmonocarboxylic acid. As used herein, the term "dimer acid" includesthose containing such amounts of these materials. Most useful is thepresent compositions are products that contain mostly dibasic acid andnone or low amounts of tribasic and monobasic acids.

Aliphatic dicarboxylic acids are seen to provide additional advantages.In particular, while not wishing to be bound by theory, it is presentlyunderstood that epoxy-polyester resin graft copolymers prepared fromepoxy ester resin precursors derived therefrom wet the substrate surfacebetter and provide enhanced adhesion between the substrate and the curedcoating. They also flow better and, thus, provide an excellent smoothsurface upon being cured. Also, the aliphatic units provide enhancedflexibility to the cured coating, as noted above, and this flexibilityof the coating is seen to provide enhanced impact resistance, a featureeven more highly desirable for chip resistant coating embodiments.

Where corrosion protection for the substrate is important, it may bepreferred to employ dicarboxylic acid according to formula (II) above,wherein R"' is, at least in part, aromatic. As noted above, it isbelieved that such aromatics in the coating composition of theinvention, such as a primer composition for a metal substrate, are moreresistant to hydrolysis than are aliphatics and, therefore, provideenhanced corrosion and moisture resistance. Of course, as also notedabove, according to preferred embodiments of the eposy ester resinprecursor, described above, the diepoxide reactant provides aromaticunits to the resin and this would similarly contribute to corrosion andmoisture resistance.

Other suitable dicarboxylic acids for the epoxy ester resin of thepresent invention will be apparent to the skilled of the art in view ofthe present disclosure.

Preferably, the chain extended diepoxide to be terminated by the acidcomponent has a number average molecular weight (M_(n)) between about1,200 and about 3,500, and more preferably between about 1,600 and about2,400.

(iv) Acid Component Reactant

The acid component comprises primary hydroxy functional acid. Numeroussuitable primary hydroxy functional acids will be apparent to theskilled of the art in view of the present disclosure, including manywhich are readily commercially available. These include C₃ -C₂₆ primaryhydroxy functional acids, wherein the acid contains one carboxyl groupand one or more hydroxyl groups (at least one of which is a primaryhydroxyl group) and no other functional groups which would substantiallyinterfere with the preparation of the hydroxyl functional epoxy estercopolymer resin, i.e., no other functional groups which would reactsubstantially with the chain-extension reactants described above or withthe chain-extension reaction product. Preferred primary hydroxyfunctional acids correspond to the general chemical formula: ##STR3##wherein R₁, R₂, R₃ and R₄ are the same or different and each preferablyis lower alkylene such as methylene or ethylene, and Z and Z' areselected independently from hydrogen, hydroxyl, and any othernon-interfering functionality such as nitrile ester group, halogen,amide, etc. Suitable hydroxy acids which may be employed in the chainterminating reaction include, but are not limited to, dimethylolpropionic acid which is most preferred, bis(hydroxy ethyl) pripionicacid, bis(hydroxy propyl) propionic acid, and the like and a compatiblemixture of any of them. Preferably, the primary hydroxy acid containstwo or more hydroxyl groups, e.g., at least one of Z and Z' contains ahydroxyl group.

Optionally, the acid component may further comprise fatty acid. Suitablefatty acids include numerous commercially available fatty acids such as,for example, those derived from or contained in either animal orvegetable fat or oil. Preferred are fatty acids from about 8 to about 18carbons, since these are found to provide flexibility to the curedcoating. Also preferred among the fatty acids are the more saturatedfatty acids, since it appears that olefinic unsaturation in the fattyacid can undergo a polymerization-type reaction between such doublebonds during the synthesis of the epoxy ester resin of the invention.Unsaturated fatty acids are suitable for use, however, such as, forexample, oleic acid, linoleic, linolenic and the like and mixtures ofsuch acids, and can be used together with a suitable inhibitor for thepolymerization-type reaction such as hydroquinone or the like, of whichmany are commercially available and will be apparent to the skilled ofthe art in view of the present disclosure. In addition, aromatic fattyacids are commercially available and can be employed. Preferred for useare the substantially saturated fatty acids such as Soya fatty acidwhich is most preferred, and butyric, lauric, palmitic and stearic fattyacids and the like or a compatible mixture of any of them. These arerelatively inexpensive and have been found to provide good reactivitywith the preferred diepoxides described above. For convenience of use,the fatty acids which are semisolid or liquid at room temperature aregenerally preferred over the solid fatty acids.

The hydroxy functional epoxy ester resin precursor used to initiatelactone polymerization in the preparation of the hydroxy functionalepoxy-polyester graft copolymer of the invention can be made accordingto techniques well known to the skilled of the art. The chain extensionand chain termination reactions may be carried out sequentially, withthe chain extension of the diepoxide being carried out first. Accordingto the sequential technique, diepoxide, diphenol and dicarboxylic acidare charged into a suitable reactor and heated. The reactants are usedin relative proportions to yield a chain extension reaction productbearing two unreacted epoxy groups and preferably substantially nounreacted carboxyl or phenol functionality. Suitable separationtechniques are known to the skilled of the art for removal of unusedreactants. It should te recognized that to assure rapid and/or morecomplete reaction of the diepoxide and with the diphenol anddicarboxylic acid functionality, it is usually preferred to have acatalyst present. The use of catalyst has been found to provideadvantageous epoxy ester resin of the invention and is preferred. Epon829 (trademark), mentioned above, as sold, provides a proprietarycatalyst. Epon 828 (trademark), is substantially the same but does notprovide such catalyst. Suitable catalysts are commerically available andinclude any of the well known catalysts for epoxy-phenol andepoxy-dicarboxylic acid reactions such as, for example, sodium carbonatewhich is preferred, and lithium neodecanoate, lithium naphthenate,lithium nanoate, other known organometallic catalysts and tertiary aminecatalysts and the like or a compatible mixture of any of them. Stillother preferred catalysts include formylmethylene triphenylphosphorane,formylmethyltriphenyl phosphorium chloride, methyltriphenylphosphoniumiodide, ethyltriphenylphosphonium acetate. Other suitable catalysts willbe apparent to the skilled of the art in view of the present disclosure.

The reaction mixture is heated to at least about 140° C. (250° F.). Whenin the presence of catalyst, exothermic reaction will proceed with orwithout further heating. Typically, the reaction mixture will then reachabout 149° C.-176° C. (300° F.-350° F.), depending upon the batch sizeand reactor vessel insulation, etc. In the absence of catalyst, suchexotherm is typically not observed and continued heating is required.The progress of the reaction can be followed by acid number measurementsand/or weight per epoxide (WPE).

As noted above, the diepoxide is reacted substantially simultaneouslywith diphenol and dicarboxylic acid in amounts sufficient to give aweight per epoxide (WPE) of between about 500 and about 2,500,preferably between about 500 and about 1,500. Preferably, the acid anddiphenol reacted with the diepoxide are employed in a ratio of fromabout 10:90 to about 90:10.

After completion of the above chain extension reaction of diepoxide withthe diphenol and dicarboxylic acid, the acid component is charged intothe reaction vessel. The reaction is exothermic and drives itself tocompletion. The chain extended reaction product is reacted with the acidcomponent in chain terminating reaction in approximately 1 to 1equivalent ratio. This ratio is preferred since excess epoxy couldresult in gelation of the reaction mixture, while excess acid componentremaining in the reaction mixture could compete with the epoxy esterresin precursor for lactone monomers during formation of theepoxy-polyester graft copolymer. For this reason, if excess acidcomponent is used during formation of the precursor, it shouldpreferably be removed prior to reaction of the precursor with lactonemonomers.

Alternatively the hydroxy functional epoxy ester resin precursor may bemade by a simultaneous technique, whereby the reactants are combined andreacted in a single batch. Due to the relative reactivity of thefunctional groups, the chain extension, where necessary, and the chaintermination reactions will both take place. If the reactions are carriedout simultaneously, the reactants are used in amounts suitable to yieldthe desired reaction ratio in view of the relative reactivity of thedicarboxylic acid and the acid component, and in view of the desiredmolecular weight for the reaction product. It appears that presentinvention compositions comprising graft copolymers made by thesimultaneous reaction technique have lower viscosity, and are thus moreeasily sprayable, than similar compositions having the same solids leveland comprising such graft copolymers made by the sequential reactiontechnique.

(v) Lactone Monomers

The lactone reactant may be any lactone, or combination of lactones,having at least six carbon atoms, for example, from six to eight carbonatoms, in the ring and at least one hydrogen substituent on the carbonatom which is attached to the oxy group in said ring. In one aspect, thelactone used as a reactant can be represented by the general formula:##STR4## in which n is at least four, for example, from four to six, atleast n+2R's are hydrogen, and the remaining R''s are substituentsselected from the group consisting of hydrogen, alkyl, cycloalkyl,alkoxy and single ring aromatic hydrocarbon radicals. Lactones havinggreater numbers of substituents other than hydrogen on the ring, andlactones having five or less carbon atoms in the ring, are consideredunsuitable for the purposes of the invention because of the tendencythat polymers thereof have to revert to the monomer, particularly atelevated temperature.

The lactones preferred in this invention are the epsilon-caprolactoneshaving the general formula: ##STR5## wherein at least six of the R's arehydrogen and the remainder are hydrogen, alkyl, cycloalkyl, alkoxy orsingle ring aromatic hydrocarbon radicals, none of the substituentscontain more than about twelve carbon atoms, and the total number ofcarbon atoms in the substituents on a lactone ring does not exceed abouttwelve. Unsubstituted epsilon-caprolactone, in which all the R's arehydrogen, is derived from 6-hydroxyhexanoic acid and is most preferred.Substituted epsilon-caprolactones, and mixtures thereof, are availableby reacting a corresponding substituted cyclohexanone with an oxidizingagent such as peracetic acid.

Among the substituted epsilon-caprolactones considered most suitable forthe purposes of the invention are the various monoalkylepsilon-caprolactones such as the monomethyl-, monoethyl-, monopropyl-,monoisopropyl-, etc. to monododecyl epsilon-caprolactones; dialkylepsilon-caprolactones in which the two alkyl groups are substituted onthe same or different carbon atoms, but not both on the epsilon carbonatom; trialkyl epsilon-caprolactones in which two or three carbon atomsin the lactone ring are substituted, so long as the epsilon carbon atomis not distributed; alkoxy epsilon-caprolactones such as methoxy andethoxy epsilon-caprolactones; and cycloalkyl, aryl, and aralkylepsilon-caprolactones such as cyclohexyl, phenyl and benzylepsilon-caprolactones.

Lactones having more than six carbon atoms in the ring, e.g.,zeta-enatholactone and eta-caprylolactone may also be polymerized inaccordance with the invention.

Polymerization of the lactones in accordance with this invention iscarried out in conventional manner in that the polymerization isinitiated by reaction with a compound having at least one reactivehydrogen capable, with or without the aid of a catalyst, of opening thelactone ring and adding it as an open chain without forming water ofcondensation--in this case the initiator compound being the hydroxyfunctional epoxy ester precursor described above.

The polymerization reaction mixture comprises between about 10 and about80 weight percent of the hydroxy functional epoxy ester resin andbetween about 90 and about 20 weight percent of the lactone monomers.Preferably, the polymerization reaction mixture comprises between about35 and about 65 weight percent hydroxy functional epoxy ester resin andbetween about 65 and about 35 weight percent lactone monomers.

To initiate and continue the polymerization of the lactone, the lactoneand the initiator (i.e., the precursor) are preferably heated to atemperature between about 130° and 200° C. in order to achieve apractical and desirable rate of reaction with a minimum ofdecomposition. The temperature may be considerably lower however, i.e.,as low as about 50° C. at the sacrifice of speed of reaction. It mayalso be considerably higher, i.e., up to about 300° C., although caremust be taken at such higher temperatures because of the more likelylosses, at temperatures above 250° C., due to decomposition orundesirable side reactions. Generally, therefore, a temperature range of50° to 300° C. is considered operable and a more limited range betweenabout 130° and 200° C. is considered preferable.

The polymerization may be, and preferably is, carried out with the useof a catalyst, such as a basic or neutral ester interchange catalyst, toaccelerate the reaction. Among catalysts suitable for this purpose aresuch metals as lithium, sodium, potassium, rubidium, cesium, magnesium,calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium,tin, lead, antimony, arsenic and cerium, as well as the alkoxidesthereof. Additional suitable catalysts are, by way of example, thecarbonates of alkali- and alkaline earth metals, zinc borate, leadborate, zinc oxide, lead silicate, lead arsenate, litharge, leadcarbonate, antimony trioxide, germanium dioxide, cerium trioxide,cobaltous acetate and aluminum isopropoxide. Catalyst concentrationsbetween about 0.001 and 0.5%, based on the weight of the startinglactones, are suitable. The preferred range is from 0.01 to 0.2%.

The hydroxy functional epoxy-polyester graft polymerization productsobtained in accordance with the invention have molecular weightsgenerally upwards of about 2,000 and preferably within the range ofabout 4,000 to about 20,000, although molecular weights below andsubstantially above this range are obtainable if desired. Also, whilenot wishing to be bound by theory, it presently is understood that thechemical structure of the hydroxy functional epoxy-polyester graftcopolymer is as follows. They have reactive terminal hydroxyl orcarboxyl groups, the number of reactive terminal groups depending uponthe functionality of the initiator. Further, it presently is understoodthat they are characterized by the presence of series of interconnected,substantially linear units or groups composed of carbon, hydrogen andoxygen. The interconnected units are opened lactone residues each havinga terminal oxy group at one end, a carbonyl group at the other end, anintermediate chain of at least five carbon atoms and at least onehydrogen substituent on the carbon atom in the intermediate chain thatis attached to the terminal oxy group. The oxy group of one lactoneresidue is connected to the carbonyl group of an adjacent lactoneresidue in the series and the oxy group of the last lactone residue in aseries is connected to a hydrogen to form a terminal hydroxyl group atone end of the series.

B. Crosslinking Agent

The crosslinking agent employed in the novel solvent based coatingcompositions of the invention comprises blocked polyisocyanate. Thenovel solvent based coating compositions of the invention, as a resultof employing blocked polyisocyanate crosslinking agents, exhibitexceptional shelf stability even when corrosion inhibiting pigments suchas zinc chromate are used in high concentrations.

As used herein "blocked polyisocyanate" means an isocyanate compoundcontaining two or more isocyanato groups, all of which have been reactedwith a material which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general the blocked polyisocyanate may beprepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure that no freeisocyanate groups are present. The blocking agent may be represented bythe formula BH and may be selected from numerous materials, hereinafterdiscussed, which bear an active hydrogen.

The blocked polyisocyanate crosslinking agent is included incompositions of the invention in amounts such that upon deblocking ofthe blocked isocyanate groups at the cure temperature of thecomposition, the crosslinking agent provides between about 0.5 and about1.6, preferably between about 0.8 and about 1.3, reactive isocyanategroups per reactive group on the film forming resin of the coatingcomposition as described above. Blocked polyisocyanates of numeroustypes may be employed in the compositions of the invention. Particularlysuitable blocked polyisocyanates, which will be discussed furtherhereinafter, include blocked polymethylene polyphenol isocyanates,isocyanurate ring containing blocked polyisocyanates and certainoligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examples arethe aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidine and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'-tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; trimethylolpropane, pentaerythritol, andthe like, as well as mono-ethers such as diethylene glycol, tripropyleneglycol and the like and polyethers, i.e., alkylene oxide condensates ofthe above. Among the alkylene oxides that may be condensed with thesepolyols to form polyethers are ethylene oxide, propylene oxide, butyleneoxide, styrene oxide and the like. These are generally calledhydroxyl-terminated polyethers and can be linear or branched. Examplesof polyethers include polyoxyethylene glycol, polyoxypropylene glycol,polyoxytetramethylene glycol, polyoxyhexamethylene glycol,polyoxynonamethylene glycol, polyoxydecamethylene glycol,polyoxydodecamethylene glycol and mixtures thereof. Other types ofpolyoxyalkylene glycol ethers can be used. Especially useful polyetherpolyols are those derived from reacting polyols such as ethylene glycol,diethylene glycol, triethylene glycol, 1,4-butylene glycol, 1,3-butyleneglycol, 1,6-hexanediol, and their mixtures; glycerol, trimethylolethane,trimethylolpropane, 1,2,6-hexanetriol, pentaerythritol,dipentaerythritol, tripentaerythritol, polypentaerythritol, sorbitol,methyl glucosides, sucrose and the like with alkylene oxides such asethylene oxide, propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR6##wherein n equals 1 to 3. Such compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Mich., have proven to beparticularly useful in compositions of the invention, resulting incompositions exhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Representative of those blocking agents which are preferred are thoseselected from the group consisting of (i) aliphatic, cycloaliphatic andaromatic alkyl monoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv)lactams; and (v) triazoles. Any suitable aliphatic, cycloaliphatic oraromatic alkyl monoalcohol may be used as a blocking agent in accordancewith the present invention. For example, aliphatic alcohols, such asmethyl, ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl,nonyl, 3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the likemay be employed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are epsilon-caprolactam,epsilon-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class type of blocked polyisocyanatecrosslinking agent which may be employed in the novel solvent basedcoating compositions of the invention comprises isocyanurate ringcontaining blocked isocyanate compounds. In general, these blockedpolyisocyanates may be formed by blocking with the aforementionedblocking agent isocyanurate ring containing polyisocyanates. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available.

A particular desirable blocked polyisocyanate crosslinking agent is theblocked form of the pure trifunctional isocyanurate represented by thefollowing formula: ##STR7## wherein R is selected from the groupconsisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. Pat. No. 4,491,633, the disclosure of which is incorporatedherein by reference.

(ii) Oligoester Modified Blocked Polvisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the novel solvent based coating compositions of this inventionare oligoester modified blocked polyisocyanates prepared from aparticular class of oligoester diols and triols. A first type of sucholigoester modified blocked polyisocyanates is prepared from organicdiisocyanates bearing one isocyanate group more reactive than the other,with the more reactive isocyanate first being blocked with a blockingagent and the remaining isocyanate group then being reacted withhydroxyl functionality of an oligoester diol or triol as referred toabove. The second type of oligoester modified blocked polyisocyanate maybe prepared by reacting oligoester diols from the aforementioned classof oligoester with an excess of organic diisocyanate so as to form anisocyanate terminated prepolymer followed by blocking of the terminalisocyanate groups of the prepolymer with an active hydrogen containingblocking agent. Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting outstanding flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issued Mar.30, 1982, the disclosure of which is hereby incorporated by reference.The hydroxy functional oligoesters within the useful class of materials(i) have a number average molecular weight (Mn) between about 150 andabout 3000, preferably between about 230 and about 1000, (ii) bear 2 or3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide;

(b) the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and mono- or polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of monocarboxylic acid andhydroxy functional mono- or polyepoxide, preferably monoepoxide, and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanate group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyante and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate crosslinking agents useful in compositionsof the invention. The organic polyisocyanate-blocking agent adductintermediate is formed by reacting a sufficient quantity of the blockingagent with the organic diisocyanate to insure that one of the two --NCOgroups on the diisocyante is reacted. The reaction between the organicdiisocyanate and the blocking agent is exothermic; therefore, thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

This intermediate is next reacted with the oligoester diol or trioldescribed above so as to react substantially all free or unblockedisocyanate groups of the diisocyanate/blocking agent intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanategroups formed on the resultant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanate groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanato group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

C. General Discussion--Other Aspects of Invention and Other Components

The coating compositions of the invention have been found to provide acured coating having the advantageous physical properties describedabove, over a wide range of cure temperatures and a wide range of solidslevels. More specifically, the coating compositions according topreferred embodiments of the invention have been found to cure attemperatures from as low as about 120° C. or less within about 15minutes or less, and yet to cure and suffer no significant loss ofadvantageous physical properties at temperatures as high as about 200°C. or more for periods up to about 60 minutes or more. Consideredtogether with the storage stability of the coating composition, it canbe readily recognized that the present invention provides a highlysignificant advance in the coating composition art.

It will be within the skill of the art to determine the proper volatileorganic content for a given coating composition of the invention and fora given application. Preferred solvents have relatively low volatilityat temperatures appreciably below their boiling points such that solventevaporation is low during storage and/or application of the coatingcomposition to the substrate. A suitable solvent system may include, forexample, toluene, methyl ethyl ketone, isobutyl acetate, xylene,cellosolve acetate, acetone and a mixture of any of them. Other solventswhich may be employed include terpenes, aliphatic and aromatic naphthas,and the like. Additional suitable solvents are commercially availableand will be apparent to the skilled of the art in view of the presentdisclosure.

Any solvent allowed to remain in the cured coating should be inert so asto avoid adverse effect upon the cured coating or upon another coatinglayer used in conjunction with it during the curing process orthereafter. Preferrably, the cured coating is substantially free ofsolvent.

Sufficient solvent is used to reduce the viscosity of the coatingcomposition to a level suitable for application to the substrate in thedesired manner.

Obviously, in those cases where the composition is to be applied as achip resistant primer the amount of solvent will be reduced so as togive a solids level of about 65-80%. Such higher solids materials aregenerally applied using hot spray equipment.

Flow control agent(s), for example, polybutyl acrylate; wettingagent(s), for example, silicone; pigments; pigment dispersants;corrosion inhibitors, for example, chromate pigments, numerous of all ofwhich are known to the skilled of the art, may be employed in thecoating compositions of the invention. In addition, suitable reactiveadditives can be used, including, for example, low molecular weight diolflow control agents and reactive diluents. Compositions of theinvention, and in particular the chip resistant primers of theinvention, may also include anti-settling or anti-sagging agents tocontrol the thixotropic properties of the composition. Exemplary ofavailable materials suitable for this purpose are Dislon (trademark)6900-20X manufactured by Kusumoto Chemicals, Ltd., Tokyo, Japan and soldby King Industries, Norwalk, CT. 06852; Bentone (trademark) 38, N. L.Industries, Highstown, N.J. 08520; and Cab-O-Sil (trademark) M-5, CabotCorporation Boston, Mass.

Curing the coating composition requires baking for sufficient time atsufficiently elevated temperature to react the crosslinking agent withthe hydroxyl functionality of the hydroxy functional epoxy-polyestergraft copolymer. The time and temperature required to cure the coatingare interrelated and depend upon the particular hydroxy functionalepoxy-polyester resin, crosslinking agent, solvent and other materials,if any, and the amount of each comprising the coating composition. Thecoating compositions according to preferred embodiments of theinvention, as described above, have been found to provide the bestcoating results when cured at temperature at about 150° C. (300° F.) for20 minutes. It is a highly significant advantage of the invention,however, that these same coating compositions can withstand, forexample, temperature as high as about 200° C. (390° F.) for periods oftime as long as about 60 minutes. Accordingly, great flexibility isprovided in both designing and implementing a curing schedule for partscoated with the coating compositions of the invention. Thus, in theassembly of automotive vehicles, for example, vehicles unavoidably heldin a curing oven for long periods of time during unplanned assembly lineshut-downs are recovered with cured and unharmed coatings.

High solids coating compositions according to the present invention,comprising the novel crosslinkable hydroxy functional epoxy-polyestergraft copolymer resins of the invention, especially the preferred resinsdescribed above and blocked polyisocyanate crosslinking agent,especially the preferred materials described above, have been found toafford cured coatings with improved corrosion resistance and chipresistance, thus representing a highly advantageous advance in the art.

A most preferred use of the coating composition of the invention is as ahigh solids hot sprayable chip resistant primer for use on a bare metalsubstrate such as for an automotive vehicle body which is subject tochipping. Primer compositions typically are pigmented and any pigmentscommonly included in primer compositions for metal substrates andacrylic dispersion topcoats such as, for example, carbon black, ironoxide, lithopone, magnesium, silicate, silica, barium sulfate, TiO2,chrome yellow, calcium chromate, strontium chromate, zinc potassiumchromate any the like may be used. The primer can be pigmented accordingto known methods including, for example, by grinding pigments in aportion of the curable resin and adding to the primer composition.

The pigment-to-binder ratio of the chip resistant primer may be fromabout 0.5:1 to about 2:1 by weight, respectively; it is preferred,however, to use a primer having a pigment-to-binder ratio of from about1:1 to about 1.5:1 by weight, respectively.

In preferred embodiments of this invention pigments and thixotropicagents desireably are dispersed with epoxy ester resins which do nothave an elastomeric component as does the hydroxy functionalepoxy-polyester graft copolymer employed as the primary film formingresin of the compositions. It has been found that in addition to beingvery effective dispersing agents for the preparation of pigmentmillbases and thixotropic dispersions, non-elastomeric epoxies give thecompositions toughness. One type of epoxy useful for this purposecomprises the reaction product of diepoxide, dimer acid and a mixture ofSoya fatty acid and propionic acid (See Example 5). Other epoxy esterresins useful for this purpose are those disclosed in U.S. applicationsSer. Nos. 448,886 filed June 14, 1982 (abandoned), 431,465 filed Sept.30, 1982 (abandoned) and in U.S. Pat. No. 4,491,641, all assigned to theassignee of this application. These resins comprise the simultaneousreaction product of diepoxide with (i) diphenol, dicarboxylic acid or amixture of them in chain extension reaction and (ii) fatty acid in chainterminating esterification reaction. Still other suitable epoxy resinsuseful for dispersing pigment and thixotropic agents will be apparent tothe skilled of the art in view of the present disclosure.

No special expedients are necessary in formulating the primercompositions of this invention. For example, they may be prepared simplyby incorporating the resinous components in a suitable solvent system.Thus, for example, by suitable mixing or agitation, each resinouscomponent may be dissolved in a solvent and the resulting solutionscombined to form finished primer compositions.

The solvent system may be any suitable combination of organic solventsas described above. For a hig solids, hot sprayable, automotive vehiclechip resistant primer, the solvent will comprise preferably about 20 toabout 40 percent by weight of the total coating compositions, althoughof course, larger or smaller amounts may be utilized depending upon thesolids content desired.

The primer is generally maintained at about 65 to about 80 percentsolids content for hot spraying purposes with conventional thinners suchas aromatic hydrocarbons, commercial petroleum cuts which areessentially aromatic, and the like, and sprayed onto the metal base orother substrate and cured. The primer may be applied in greaterthickness of 1 to 25 mils wet, preferably 10 to 25 mils wet, in order toobtain final coatings in the desired range of 5-11 mils in regionshighly susceptible to chipping and is then feathered down in thicknessto the thickness of paints in areas not receiving a chip resistantprimer. The primer is cured at elevated temperatures by any convenientmeans such as baking ovens or banks of infra-red heat lamps. Curingtemperatures are preferably from about 135° C. to about 165° C.,although curing temperatures from about 100° C. to about 230° C. may beemployed, if desired.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that the specific examplesare presented by way of illustration and not by way of limitation.Unless otherwise specified, all references to "parts" are intended tomean parts by weight.

EXAMPLE 1 Preparation of Hydroxy Functional Epoxy-Polyester GraftCopolymer

In a suitable reactor were charged 304 parts Epon 829 (trademark), ShellCHemical Co., diepoxide, 150 parts Empol 1016 (trademark, Emery Ind.,Inc., dimer acid), 61 parts bisphenol-A, 70 parts 2,2-bis(hydroxymethyl)propionic acid, and 4 parts lithium neodecanoate. The mixture was heatedto 160° C. slowly, and maintained there until acid number was lessthan 1. 1008 parts epsilon-caprolactone, 400 parts Solvesso 150, and 3parts dibutyl tin oxide were added to the mixture. The temperature wasraised to 130° C., at which point a mild exothermic reaction occurs thatraises the temperature to 175° C. The progress of the reaction wasfollowed by viscosity and % non-volatile solids measurement; after twohours the viscosity was M-R (20 parts mixed and 12 parts Solvesso 150yielding a 50.0% solids solution). At this point, heating was removedand 280 parts Solvesso 150 is added; the mixture was allowed to cool.The resulting product has Z₅ viscosity at 70.0% solids.

EXAMPLE 2 Preparation of Hydroxy Functional Epoxy-Polyester GraftCopolymer

In a suitable reactor were charged 470 parts Epon 829 (trademark, ShellChemical Co., diepoxide), 230 parts Empol 1016 (trademark, Emery Ind.,Inc., dimer acid), 46 parts bisphenol-A, 112 parts Soya fatty acid, 107parts 2,2-bis(hydroxymethyl) propionic acid, and 5 parts lithiumneodecanoate. The temperature of the mixture was raised to 170° C.; anexothermic reaction occurs which raises the temperature to about180°-190° C. 20 parts xylene was added to strip out any residual water.After one hour the acid number was 1. 1450 parts epsilon-caprolactone,270 parts Solvesso 150, and 3 parts dibutyl tin oxide were added to themixture. The temperature was raised to 130° C., at which point a mildexothermic reaction takes place that raises the temperature to 175° C.,and maintained there for two hours. The % solids of the mixture wasdetermined (88.0%). At this point, the heat was removed; 730 partsSolvesso 150 was added, and the mixture was allowed to cool. Theresulting product has a Z₅ viscosity at 70.0% solids.

EXAMPLE 3 Preparation of Hydroxy Functional Epoxy-Polyester GraftCopolymer

In a suitable reactor were weighed 585 parts Epon 829 (trademark, ShellChemical Co., diepoxide), 116 parts bisphenol-A, 286 parts Empol 1016(trademark, Emery Ind., Inc., dimer acid), 134 parts2,2-bis(hydroxymethyl) propionic aicd, and 3 parts lithium neodecanoate.The temperature of the mixture was heated to 170° C., at that point anexothermic reaction occurs which remains the temperature to 180°-190° C.After one hour the acid number was less than 3. 1680 partsepsilon-caprolactone, 310 parts Solvesso 150, and 2 parts of dibutyl tinoxide were added to the mixture. The temperature of the mixture wasraised to 130° C., at which point a mild exotherm occurs that raises thetemperature to about 160° C., and maintained there for two hours. The %solids of the mixture was determined (88%). At this point, heat wasremoved; 390 parts M-pyrol was added, and the mixture was allowed tocool. The resulting product has a Z₇ viscosity at 80.0% solids.

EXAMPLE 4 Preparation of Hydroxy Functional Epoxy-Polyester GraftCopolymer

In a suitable reactor were charged 582 parts of Eponex (trademark, ShellChemical Co., diepoxide), 137 parts of bisphenol A, 168 parts of Empol1016 (trademark, Emery Ind., Inc., dimer acid) and 0.5 parts of sodiumcarbonate. The mixture was heated up to 160° C. slowly and maintainedthere until the acid number was less than one. At this point 114 partsof 2,2-bis(hydroxy methyl)propionic acid and 0.5 part of sodiumcarbonate were added. The temperature was raised then to 160° C. andkept there until the acid number dropped below 5. 667 parts ofepsilon-caprolactone and one part of dibutyltin oxide were added to themixture. The temperature was kept at 150° C. for two hours and then themixture was thinned with 1111 parts of M-pyrol. The final product hadviscosity of T at 58.6% solids.

EXAMPLE 5 Preparation of Epoxy-Ester Dispersing Resin

Into a suitable reactor were charged 1380 parts Epon 829 (trademark,Shell Chemical Co., diepoxide), 954 parts Empol 1016 (trademark, EmeryInd., Inc., dimer acid), 364 parts Soya fatty acid, 268 parts 2,2bis(hydroxymethyl)propionic acid, and 13 parts lithium neodeconoate. Thetemperature of the mixture was brought up to about 180° C., at whichpoint an exothermic reaction took place that raised the temperature toabout 200° C. After one hour, the acid number was found to be less than2. 940 parts Solvesso 100 and 305 parts Solvesso 150 were added, and themixture was cooled. The resin had a viscosity of Z₇ at 70.0% solids.

EXAMPLE 6 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor were charged 780 parts methylethyl ketoxime. 180parts Solvesso 100. 1330 parts of PAPI 27 (trademark, UpJohn ChemicalCo., aromatic polyisocyanate) was added dropwise to the mixture over twohours; the reaction temperature rose from room temperature to 80°-95° C.39 parts 2-ethylhexanol was added to the mixture and the temperature ofthe mixture was maintained at 85° C.-95° C. for one hour. At that point,816 parts M-pyrol was added and the mixture was cooled. The resultingresin was dark brown and had a viscosity of 6000 cps at 67.0% solids.

EXAMPLE 7 Preparation of Blocked Polyisocyanate Crosslinking Agent

Into a suitable reactor was charged 537 parts methylethyl ketoxime. 784parts PAPI 94 (trademark, UpJohn Chemical Co., aromatic polyisocyanate)was added dropwise over two hours; the reaction temperature rose fromroom temperature to 80° C.-95° C. The mixture was maintained at 85°-95°C. for one hour. At that point, 300 parts methylamyl ketone and 150parts M-pyrol were added and the mixture was cooled. The resulting resinwas dark brown and was 75.0% solids.

EXAMPLES 8-11 Preparation of Blocked Polyisocyanate Crosslinking Agent

Blocked isocyanate crosslinkers according to the invention were preparedin the manner of Example 7. The components employed are shown in thetable below.

    ______________________________________                                                      Example                                                                       8    9         10     11                                        Composition     Parts                                                         ______________________________________                                        L-2991 A*       360    360       360                                          Desmodur IL*                          525                                     methyl amyl ketoxime                                                                          174                    87                                     benzotriazole          238                                                    epsilon-caprolactam              228                                          N--methyl pyrolidone                                                                          133    150       195  461                                     % solids         80    80.1      75.1  57                                     Viscosity       Z.sub.1                                                                              Z.sub.6   Z.sub.2                                                                            Z                                       ______________________________________                                         *Trademarks of Mobay Chemical Co.; L2291 A is a biurette of hexamethylene     diisocyanate; Desmodur IL is a polyisocyanurate of tolylene diisocyanate.

EXAMPLE 12 Millbase Preparation

In a one gallon can or ballmill were charged the following materials andone quart of diagonal shot. The mixture was placed on a roller mill for16-24 hours to reach a 7+ hegman dispersion. At that point, the letdownwas added, and the mixture was run an additional hour on the rollermill.

    ______________________________________                                        Hi-Sol #3*                585                                                 2-Ethyl Hexanol           95                                                  Polyethylene Wax          70                                                  Anti-Terra-U**            40                                                  Resin of Example 5        103                                                 Barytes                   2259                                                TiO.sub.2                 429                                                 Carbon Black              29                                                  Strontium Chromate        143                                                 Letdown: Resin of Example 5                                                                             247                                                 ______________________________________                                         *Trademark of Ashland Chemical Co., Columbus, Ohio; HiSol #3 is an            aromatic solvent.                                                             **Trademark of Byk Mallinckrodt, Wallingford, CT 06492; AntiTerra-U is an     antisettling and wetting agent.                                          

EXAMPLE 13 Bentone Gel Preparation

To a clean Ball Mill, charge the following:

    ______________________________________                                                              Parts                                                   ______________________________________                                        Solvesso 150            513                                                   Propylene Carbonate     13                                                    Bentone 38              30                                                    Grind 30 minutes, then add:                                                                           384                                                   Resin of Example 5                                                            Grind approximately 2 Hrs. to 8 Hegman.                                       Letdown with: Solvesso 150                                                                            60                                                                            1000                                                  ______________________________________                                    

    ______________________________________                                        Coating compositions of the invention were formulated                         as shown below:                                                                             Example                                                                       14   15      16     17    18                                    Composition     Parts                                                         ______________________________________                                        Resin of Example 1                                                                            2635                                                          Resin of Example 2     2635    2635                                           Resin of Example 3                  2241                                      Resin of Example 4                        3180                                Millbase of Example 12                                                                        5788   5788    5788 5788  5788                                Bentone Gel of Example 13                                                                     2315   2315    2315 2315  2315                                Crosslinker of Example 6                                                                       984    984          984   984                                Crosslinker of Example 7       1050                                           Dislon*          114    114     120  120                                      Cab-O-Sil**      142    142                150                                ______________________________________                                         *Trademark Kusumoto Chemicals, Ltd., Dislon is an antisagging agent           **Trademark of Cabot Corp., Boston, Mass., CabO-Sil is a foamed silica        (antisettling agent).                                                    

The coating compositions were prepared by sequential mixing in a 5gallon working capacity EMCO Proto-Lab SW Mill (trademark), Epworth Mfg.Co., South Haven, Mich., set at 900 rpm. Resin and Dislon (trademark)were first mixed for approximately 10 minutes and then millbase, BentoneGel and crosslinker were added sequentially while mixing. FinallyCab-O-Sil (trademark) was added and the composition mixed until a grindof 6+ on the Hegman scale was obtained.

The above compositions were sprayed at 140°-160° C. using hot-sprayequipment commercially available from Nordson Corp. Unpolished Bonderitesteel panels were sprayed and baked at 135° C. for 20 minutes. Thethickness of the coating tested varied from 5 mils to 12 mils. Thepanels were top-coated with white enamel and tested for chip resistanceusing 10 pts. of gravel in the gravelometer test. All the abovecompositions exhibited excellent chip resistance. In addition, panelswere tested for corrosion resistance (500 hrs. salt spray test, scribedpanels) and humidity resistance with excellent results.

Additional coating compositions according to the invention are shownbelow.

    ______________________________________                                                       Example                                                                       19   20       21     22                                        Composition      Parts                                                        ______________________________________                                        Resin of Example 2                                                                             2635   2635     2635 2635                                    Millbase of Example 12                                                                         5788   5788     5788 5788                                    Gel of Example 13                                                                              2315   2315     2315 2315                                    Crosslinker of Example 8                                                                        922                                                         Crosslinker of Example 9                                                                               922                                                  Crosslinker of Example 10         984                                         Crosslinker of Example 11             1294                                    Dislon*           100    100      100  100                                    ______________________________________                                         *Trademark of Kusumoto Chemical, Ltd., Dislon is an antisagging agent.   

In view of this disclosure, many modifications of the invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications ccll within the true scope of this invention andbe included within the terms of the appended claims.

INDUSTRIAL APPLICATION

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as a hotsprayable, high solids coating composition suitable for use as a chipresistant automotive vehicle primer adapted for use on body panel areassubject to chipping by stones, gravel and other road debris.

What is claimed is:
 1. An organic solvent based, thermosetting coatingcomposition comprising:(I) hydroxy-functional epoxy-polyester graftcopolymer having a number average molecular weight (Mn) of between about2,000 and about 20,000, said copolymer being the product ofpolymerization of lactone monomers in the presence of hydroxy functionalepoxy ester resin precursor having a number average molecular weight(Mn) of between about 1,000 and about 4,000, said precursor being thechain extended product of diepoxide reacted substantially simultaneouslywith diphenol and dicarboxylic acid and chain terminated with an acidcomponent, said acid component reacted in approximately a 1:1 equivalentratio with the chain extended product and comprises a primary hydroxyfunctional acid, said diepoxide being reacted substantiallysimultaneously with said diphenol and dicarboxylic acid in amountssufficient to give a weight per epoxide of between about 500 and about2,500, and wherein said polymerization of said lactone monomers iscarried out at a temperature between about 50° C. and about 300° C. andthe polymerization reaction mixture comprises between about 10 and about80 weight percent said hydroxy functional epoxy ester resin precursorand between about 90 and about 20 weight percent said lactone monomers,wherein said lactone monomers are selected from those represented by thegeneral formula: ##STR8## in which n is at least 4, at least n+2 R's arehydrogen, and the remaining R's are substituents selected from the groupconsisting of alkyl, cyclolkyl, alkoxy and single ring aromatichydrocarbon radicals; and (II) blocked polyisocyanate crosslinking agentcomprising at least two isocyanate groups which have been blocked byreaction with an active hydrogen bearing blocking agent, said blockedpolyisocyanate crosslinking agent being included in an amount such thatupon deblocking of the blocked isocyanate groups thereof at the curetemperature of the composition, said crosslinking agent provides betweenabout 0.5 and about 1.6 reactive isocyanate groups per reactive group onsaid hydroxy functional epoxy-polyester graft copolymer.
 2. A solventbased, theremosetting coating composition in accordance with claim 1,wherein said diepoxide is selected from the group consisting ofbisphenol-A epichlorohydrin epoxy resin, hydantoin epoxy resin, cyclicand acyclic aliphatic diepoxides and mixtures thereof.
 3. A solventbased, thermosetting coating composition in accordance with claim 1,wherein diphenols are selected from the group consisting of bisphenol-A,bisphenol B, bisphenol-F and mixtures thereof.
 4. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid dicarboxylic acid is selected from the group consisting ofsaturated or unsaturated, cyclic or acyclic, aliphatic or aromaticdicarboxylic acids and mixtures thereof.
 5. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid dicarboxylic acid is selected from the group consisting ofsubstantially saturated, acyclic, aliphatic dimer acids of about 4-42carbons.
 6. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said primary hydroxy functional acid isselected from C₃ -C₂₆ acids bearing a single carboxyl group, at leastone primary hydroxyl group, and no additional functionality which wouldreact substantially with said chain extension reactants or reactionproduct.
 7. A solvent based, thermosetting coating composition inaccordance with claim 1, wherein said acid component further comprisesfatty acid.
 8. A solvent based, thermosetting coating composition inaccordance with claim 7, wherein said fatty acid is selected from thegroup consisting of Soya fatty acid, butyric, lauric, palmitic andstearic fatty acid and mixtures thereof.
 9. A solvent based,thermosetting coating composition in accordance with claim 1, whereinsaid lactone monomers comprise unsubstituted epsiloncaprolactone.
 10. Asolvent based, thermosetting coating composition in accordance withclaim 1, wherein said crosslinking agent consists essentially of blockedpolyisocyanate consisting of blocked aliphatic, aromatic cycloalkylene,aliphatic aromatic and nuclear substituted aromatic polyisocyanates andcompatible mixtures thereof.
 11. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent comprises blocked polymethylenepolyphenol isocyanate which prior to blocking has the formula: ##STR9##wherein n equals 1 to
 3. 12. A solvent based, thermosetting coatingcomposition in accordance with claim 1, wherein said blockedpolyisocyanate crosslinking agent is the reaction product of:(A) thereaction product of (i) organic diisocyanate represented by the formula:

    OCN--R--NCO

wherein R is selected from the group consisting of aliphatic,cycloaliphatic and aromatic radicals and combinations thereof andwherein one of the isocyanate groups thereof is a more reactiveisocyanate group than the other isocyanate group and (ii) sufficientactive hydrogen containing blocking agent to react substantially all ofsaid more reactive isocyanate group; and (B) sufficient polyol to reactall of said other isocyanate group.
 13. A solvent based, thermosettingcoating composition in accordance with claim 1, adapted to be used as achip resistant primer to be sprayed at elevated temperature, wherein thesolids level of the composition is in the range of 60-80% by weight. 14.An organic solvent based, thermosetting coating compositioncomprising:(I) hydroxy functional epoxy-polyester graft copolymer havinga number average molecular weight (Mn) of between about 2,000 and20,000, said copolymer being the product of polymerization ofepsilon-caprolactone monomers in the presence of hydroxy functionalepoxy ester resin precursor having a number average molecular weight(Mn) of between about 1,000 and about 4,000, said precursor being thechain extended product of (i) diepoxide selected from the groupconsisting of bisphenol-A epichlorohydrin epoxy resin, hydantoin epoxyresin, cyclic and acyclic aliphatic diepoxide and mixtures thereof, (ii)diphenol consisting essentially of bisphenol-A, bisphenol B, andbisphenol-F, and (iii) dicarboxylic acid consisting of substantiallysaturated, aliphatic, acyclic dimer acids of 4-42 carbons and mixturesthereof and chain terminated with an acid component said acid componentreacted in approximately a 1:1 equivalent ratio with the chain extendedproduct and comprises a primary hydroxy functional primary acid selectedfrom the group consisting of dimethylolpropionic acid,bis(hydroxyethyl)propionic acid, bis(hydroxypropylpropionic acid andmixtures thereof, said diepoxide being reacted substantiallysimultaneously with said diphenol and dicarboxylic acid in amountssufficient to give a weight per epoxide of between about 500 and about2,500, said epsilon-caprolactone monomers being selected from thoserepresented by the general formula: ##STR10## wherein at least 6 of theR's are hydrogen and the remainder are selected from the groupconsisting of alkyl, cycloalkyl, alkoxy and single ring aromatichydrocarbon radicals, wherein none of the substituents contain more thanabout 12 carbon atoms and wherein the total number of carbon atoms inthe substituents on a lactone ring does not exceed about 12, and whereinsaid polymerization of said epsiloncaprolactone monomers is carried outat a temperature between about 130° C. and about 200° C. and thepolymerization reaction mixture comprises between about 10 and about 80weight percent said hydroxy functional epoxy ester resin precursor andbetween about 90 and about 20 weight percent said lactone monomers; and(II) blocked polyisocyanate crosslinking agent comprising at least twoisocyanate groups which have been blocked by reaction with an activehydrogen bearing blocking agent, said blocked polyisocyanate beingselected from blocked aliphatic, aromatic, cycloalkylene, aliphaticaromatic, and nuclear substituted aromatic polyisocyanates and beingincluded in said composition in an amount such that upon de-blocking ofthe blocked isocyanate groups thereof at the cure temperature of thecomposition, said crosslinking agent provides between about 0.5 andabout 1.6 reactive isocyanate groups per reactive group on said hydroxyfunctional epoxy polyester graft copolymer.